how can I position an object at a moving bonehead?
You don't tell enough but if you just need a basic animation you can do it this way:


Create a 3 bone armature. Top horizontal bone is parented to right bone.





Switch to Pose mode, select the left and right bones, open the N panel (on the right of your 3D View) and in Transform > Rotation, choose the XYZ Euler mode instead of Quaternion. Create a first pose for those bones, then a second at 180° (on the Z axis for me), and in the Dopesheet click ShiftE > Linear Extrapolation. Now your bones rotate indefinitely.





Still in Pose mode, select the top bone, go in the Properties panel > Bone Constraint and give it a Track To constraint (might be a Copy Location as well) with the left bone as Target, a Head/Tail value of 1, To > Y, Space > Pose Space/Pose Space. This bone will follow the movement.